Rheology and structures of aqueous gels of diblock(oxyethylene/oxybutylene) copolymer E22B7

The phase behavior of an oxyethylene/oxybutylene diblock copolymer (E22B7) in aqueous solution was defined using three properties: yield stress (by rh eometry and tube inversion), dynamic modulus (by rheometry), and structure (by small-angle X-ray scattering). The boundary of immobile, structured gel (hard gel) was detected by all three methods, giving satisfactory agreemen t. A structural transition within the hard gel, from bcc to hex, was detect ed by rheometry and SAXS. Two types of soft gel were detected and assigned to disordered phases containing either spherical or cylindrical micelles. C omparison with results for other diblock EmBn copolymers showed a regularit y of behavior influenced largely by oxyethylene-block length, with oxybutyl eneblock length having a minor but significant role.